A very tiny form of life — microbes include bacteria, fungi, and protozoan parasites — best visualized with a microscope. The word "microbe" did not enter English usage until 1881. It was put together from Greek roots "mikros," small + "bios," life = small (form of) life.

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Any very minute organism. As originated, the word was intended as a collective term for the large variety of microorganisms then known in the 19th century; modern usage has retained the original collective meaning but expanded it to include both microscopic and ultramicroscopic organisms (spirochetes, bacteria, rickettsiae, and viruses). These organisms are considered to form a biologically distinctive group, in that the geneticmaterial is not surrounded by a nuclearmembrane, and mitosis does not occur during replication. [Fr., fr. G. mikros, small, + bios, life]

microbe — (n.) popular name for a bacterium, 1878, from Fr. microbe, badly coined ... by Sédillot [Weekley] in 1878 from Gk. mikros small (see MICA (Cf. mica)) + bios life (see BIO (Cf. bio )). It is an incorrect use of bios; in Greek the word would mean… … Etymology dictionary